Before the first of the ten plagues that God brought upon Egypt – the plague of blood – He instructed Moshe to approach Pharaoh and warn that if he did not release Benei Yisrael, “I will hereby strike the water that is in the river with my staff, and it will transform into blood” (7:17). Yet, when the time came for the plague to begin, God instructed Moshe to have Aharon strike the river to transform the water to blood (8:1). We might wonder, then, how God could have Moshe warn Pharaoh that he – Moshe – would strike the river, when in fact this miracle was wrought by Aharon.
The Gemara in Masekhet Sanhedrin (99b) raises a similar question regarding God’s command to Moshe later, in Refidim, to strike a rock to produce water using “your stick with which you struck the river” (Shemot 17:5). God speaks of Moshe having struck the river – presumably referring to the plague of blood – even though it was actually Aharon who performed this act. The Gemara explains that God attributed this act to Moshe because he had Aharon perform this act. One who persuades somebody to perform a mitzva, the Gemara establishes, is credited with having personally performed that mitzva, and thus God speaks of Moshe as having fulfilled the mission of bringing the plague of blood even though this was actually done by Aharon.
Seemingly, we would apply the Gemara’s principle to explain the verse here in Parashat Vaera, as well. Moshe informs Pharaoh that he – Moshe – would be striking the river because he would be instructing Aharon to do so, and he would thus be credited with this act.
However, the Rogatchover Gaon (Tzofnat Panei’ach) questioned whether this concept – of attributing to somebody an action done by another person at his behest – is applicable in our context. Tosafot, in Masekhet Bava Batra (82a), discuss the case of a person who sent his bikkurim (first fruits, which must be brought to the Beit Ha-mikdash) to the Temple via a messenger, and the question arises as to whether he recites the mikra bikkurim declaration which normally accompanies the mitzva bikkurim. Citing the Talmud Yerushalmi, Tosafot claim that the owner of the fruit does not recite mikra bikkurim in such a case, as he cannot say the phrase, “I have now brought the first fruits of the land.” Since he did not actually bring the fruits to the Beit Ha-mikdash, he cannot speak of himself as doing so. Apparently, despite the Gemara’s comment that a person is credited with an action he sent somebody else to do, a person cannot speak of himself as performing an action performed by somebody else, even though it was done at his behest. Others can attribute the action to him, as God spoke of Moshe as having brought the plague of blood, but one cannot speak of himself in these terms. Although the Rashbam (there in Bava Batra) does not follow this view, and maintains that an individual who sent his bikkurim with a messenger may recite this text, the question arises according to Tosafot as to how Moshe could speak of himself striking the river.
The Rogatchover Gaon answers that in truth, Moshe himself struck the river. He likely refers to a passage in the Midrash (Sechel Tov, cited in Torah Sheleima, 81*) which describes how Moshe and Aharon together brought the plague of blood upon the Egyptians, through a joint action.
Leaving aside the technical issue as to how precisely this occurred, it is perhaps worth reflecting upon this distinction between how a person describes himself and how he is described by others. As we have seen, a person can be spoken of by a third party as performing an action he commissioned, but one cannot speak of himself of performing an action done at his behest. Underlying this distinction, perhaps, is the message that we should be indulging more in praising other people than in praising ourselves. When we speak of others, we should try to give them as much credit as we can, and to praise them even for achievements for which they only indirectly facilitated. When we speak of ourselves, however, we ought to be more discerning. We may certainly take credit for and feel pride over our accomplishments, but we must avoid indulging in self-praise. Crediting ourselves too much leads us to arrogance and complacency, and thus we should be far more liberal in our praise and compliments of other people than we are in commending ourselves.